Currently employed medical imaging diagnosis apparatuses include CT apparatuses, MRI apparatuses, PET apparatuses, angiography apparatuses and the like. In using the abovementioned apparatuses to obtain diagnostic images of a patient, a chemical liquid such as a contrast medium or physiological saline is often injected into the patient's body.
The injection of the chemical liquid into the patient is performed by connecting an injection needle to a syringe filled with the chemical liquid through an extension tube, inserting the injection needle into a blood vessel of the patient, and pushing a piston of the syringe manually or with a chemical liquid injector. In this case, the tip of the injection needle may come off the blood vessel for some reason. If the chemical liquid is injected with the injection needle coming off the blood vessel, an extravascular leak or extravasation occurs in which the chemical liquid is leaked to a peripheral area outside the blood vessel.
A leak detecting sensor is used for detecting the extravascular leak. A conventional known leak detecting sensor is an optical reflective sensor as disclosed in Patent Document 1. The leak detecting sensor of this type typically has a sensor head fixed to a body surface of a patient near the position where an injection needle is inserted. The sensor head has a structure in which a pair of a light-emitting element and a light-receiving element and a circuit substrate for these elements are put in a housing. The sensor is fixed to the patient during the injection of the chemical liquid, for example using an adhesive sheet, such that a lower surface of the housing is in intimate contact with the patient. The light-emitting element and the light-receiving element are placed side by side so that the light-emitting element within the housing in intimate contact with the body surface of the patient emits light, the emitted light is reflected in the body (under the skin) of the patient, and the reflected light is received by the light-receiving element. The surface of the housing in intimate contact with the patient has an opening portion for passing the emitted light and the reflected light in order to direct the emitted light from the light-emitting element within the housing to the patient and to guide the reflected light from the patient to the light-receiving element within the housing.